Shutting down the Rustock botnet in early March appears to have had an unexpected side benefit: the Harnig botnet apparently has ceased operations.
On the very day that law enforcement authorities, with Microsoft's help, were raiding Rustock's command-and-control servers, the servers belonging to the Harnig botnet-also known as Piptea-stopped responding, according to Atif Mushtaq, a security research engineer at FireEye. Rustock used to be spread by Harnig, suggesting some kind of a relationship between the two botnets, Mustaq wrote on the company's Malware Intelligence Lab March 22.
It was rare to see Rustock using some other infection vector or network to propagate, according to Mushtaq. Microsoft's Digital Crime Unit estimated there were about a million Rustock zombies.
"Keeping in view the timing of this sudden shutdown and Harnig's obvious relationship with Rustock, it can't be a coincidence," Mushtaq said.
The stopped activity doesn't really mean much, as the command-and-control servers have not been taken down and are likely to be still under the botnet owners' control. The servers have been wiped clean of any traces that could give away their identity or location to law enforcement. The infected computers making up the botnet army remains infected, as well.
"It looks like a decision made solely by the bot herders," Mushtaq said.
Just as the Harnig zombies remain infected, so are the Rustock zombies. Even with the command-and-control servers gone, the infected machines are still out there, meaning the Rustock gang, which is still at large, can set up operations again. There is a "great chance" that Harnig will soon resume its activities, and Mushtaq wondered if the botnet would drop new Rustock instances to revive the botnet.
Knocking out Rustock had some impact on global spam volumes immediately after the raid, even though the monthly MessageLabs report for March indicated that overall volume decreased a measly 2 percent. Even though Rustock at one point had accounted for nearly half of all spam being sent, its absence is not as obvious because other botnets, namely Bagle, have increased their output to fill the void left behind.
Even so, Harnig being out of commission may have a "significant impact on worldwide malware infection levels," said Mushtaq. Like Rustock, Harnig also does not appear on Damballa's latest top 10 list of largest botnets. Infecting computers in North America.
Dismantling Harnig would be a more difficult task than Rustock was, since Harnig's command-and-control servers are scattered all over the world and not just based in the United States, Mushtaq said. According to FireEye analysis, about 45 percent of the servers were in Russia and 26 percent in the United States, but they also had a presence in China, Japan, Italy, India, Brazil, Germany, Poland and Latvia. He considered it "amazing" that even though most of the servers appeared to be hosted in safe havens, the herders still chose to suspend, even if it's only temporarily, all malicious activity.
Even though there was no immediate danger to Harnig as no one was really going after it, the Harnig bot herders panicked and felt they better go underground for a while, Mushtaq speculated.
"The Harnig and Rustock operators must have been very close to each other," he said.
Mushtaq didn't rule out the possibility that the same gang ran both Rustock and Harnig.